Whatsapp problem for Torch 9800

I have a problem with my phone. I downloaded this app from the official website, installed and working fine for a couple of days. Then, it starts to lag and freezes for no reason, especially when I'm scrolling down looking at my contacts in favourites. I did a soft and hard reset and doesn't work at all. So i ended up deleting this app and reinstall again and the problem is still happening.